Purpose :
As previously established by our lab, diabetic retinopathy (DR) is preceded by another complication of diabetes – circadian rhythm misalignment. Here we want to determine if correcting the circadian clock we can prevent DR. In this study we aligned the circadian clock by applying long term intermittent fasting (IF) as a strategy to prevent DR and examined the mechanisms that lead to protection from retina pathology.

Methods :
Type 2 diabetic mice, (db/db) and age-matched controls (db/m) were on IF feeding schedule initiated at night for 6 months. Ad-libitum groups had food at all times. At the completion of the experiment, eyes, brains, blood, spleen and bone marrow were harvested at day, ZT5 and at night, ZT17 (Zeitgeber Time). DR was assessed by enumeration of acellular capillaries. Plasma hormones, homeostasis of inflammatory monocytes and inflammatory gene expression were detected.

Results :
IF prevented diabetes-induced clock dysfunction and formation of acellular capillaries in the retina. This effect was not due to restoration of glucose levels. Rather, IF affected the circadian rhythms of inflammatory monocytes. During the fasting period of the IF regimen, monocytes were depleted by 50% from circulation independently of status of diabetes or time. The absence of Ly6Chi monocytes in the blood led to less monocytes homing to the retina during the fasting period. Yet during the feeding period, monocytes were present in the blood and homed to the retina but in reduced rates compared to ad-lib db/db or db/m mice. Similarly, IF affected the expression of inflammatory genes in the retinas of IF-treated mice. Overall, these effects were associated with a reduction of norepinephrine and nutrients in circulation (free fatty acids and triglycerides) and with an increase in corticosterone during the fasting period.

Conclusions :
Currently it is believed that monocyte circadian rhythms are governed by the sympathetic nervous system. Herein, we show for the first time that fasting versus feeding, i.e the availability of nutrients significantly governs the behavior of monocytes and drives inflammation. We postulate that the prevention of diabetic complications is associated with the reduced inflammation observed during the fasting state of the IF treatment.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.